This invention relates in general to drum support apparatus and more specifically to a drum supporting hub and a drum assembly including the hub.
It is customary in the art of electrophotography to form an electrostatic latent image on an electrophotographic imaging member comprising an electrically conductive backing such as, for example, a metallic or metal-coated cylindrical substrate having an inorganic photoconductive insulating layer applied thereto. Typical electrophotographic imaging members comprise, for example, an aluminum cylinder having a thin layer of vitreous selenium thereon. Such members are characterized by being capable of accepting and retaining a suitable uniform electrostatic charge in the dark and of quickly and selectively dissipating a substantial part of the charge when exposed to a light pattern.
As more advanced, higher speed electrophotographic copiers, duplicators, and printers are developed, stringent requirements have been placed on these complex, highly sophisticated imaging systems including long operating life with minimum maintance requirements. For example, the supporting substrate for electrophotographic imaging members must meet precise tolerance standards and adhere well to photoconductive insulating layers applied thereto. Generally, the aluminum drums utilized as supporting substrate material for rigid drum-shaped supporting substrates are relatively expensive and often require replacement due to wear prior to the need to replace the photoconductive insulating layer. For example, rapid wear, sometimes referred to as "ring gouge", is caused by spacing shoes riding on the surface of the ends of aluminum drums. Moreover, lathing and polishing of aluminum drums are necessary prerequisites to achieving a uniform surface for subsequently applied photoconductive insulating layer or layers. Moreover, aluminum drums must necessarily be thick in order to achieve adequate rigidity to meet the stringent tolerance requirements of precision machines. Heavy drums require more powerful drive systems and rugged clutches to overcome high inertia characteristics.
The precise tolerance requirements of current reproduction machines mean low photoreceptor drum radial run-out. Damage to a drum during handling can deform the drum and counterbore resulting in an out-of-tolerance condition when the drum is fitted with end support hubs. A slight cock in the drum assembly can throw the shaft support bearing off center and this can be magnified by the weight of a heavy drum. Control of drum run-out is particularly important for magnetic brush development systems in which drum tolerance directly affects the spacing between the drum and magnetic brush roller applicators.
Various attempts to reduce drum radial run-out have been attempted for rigid drums. One approach is illustrated in U.S. Pat. No. 4,105,345 to VanWagner in which adjustable flanges are fitted into internal grooves of a rigid drum to reduce wobble. In U.S. Pat. No. 4,120,576 to Babish, support hubs having outer surfaces adapted for interface fitting with the inside surface of a drum are employed to diminish circular run-out of the drum.
In U.S. Pat. No. 4,040,157 to Shanly and U.S. Pat. No. 3,994,053 to Hunt, drum support hubs having a plurality of spaced equidistant lobes located on the outer surfaces are employed to reduce the load required to properly seat the drum against the hubs thereby decreasing the possibility of drum run-out by reducing the contact area between the hub and drum. This type of arrangement would deform a flexible drum.
In U.S. Pat. No. 2,918,867, a printing collet is described wherein the end of a cylinder is provided with a threaded recess with an intermediate shoulder at the bottom of the recess and a tapered hole extending from the shoulder toward the other end of the cylinder. An externally threaded annual driving head fitted with a longitudinally tapered sleeve having a short flange at one end, a plurality of partially longitudinally extending slots equally spaced about the periphery of the tapered portion of the sleeve and terminating short of the tapered end of the sleeve and a longitudinally extending slot extending the entire length of the sleeve, is screwed into the threaded end of the cylinder to force the sleeve between the inner surface of the tapered hole and a central axial shaft.
In laid open Japanese Patent Application No. 56-185574 to Y. Fujimaki, published May 24, 1983, a cylinder of resin or electroformed nickel coated with a photosensitive layer is fitted to a shaft by means of detachable flanges which fit on the ends of the drums. The flanges appear to comprise lips which contact the ends of the drums as well as the inner surface of the drums adjacent the ends. The detachable flanges are not self centering and require precise tolerances for both the flanges and the internal diameter of the drum.
In Japanese laid open Patent Application Ser. No. 56-185679, published May 24, 1983 to H. Tokunaga, a drum similar to the drum describd in Japanese laid open Patent Application Ser. No. 56-185574 above is disclosed. This drum is fitted with a thermostatically controlled heating element. Like the flanges of Japanese laid open Patent Application Ser. No. 56-185574, the flanges are not self centering and precise tolerances are necessary.
In laid open Japanese Patent Application Ser. No. 56-185578 to Y. Fujimaki, an electroformed drum is supported on a shaft by means of flange members such as those described above with reference to application Ser. No. 56-185574 and which additionally utilizes an annular auxillary member to support the center of the drum. Like the flanges of Japanese laid open Patent Application Ser. No. 56-185574, the flanges are not self centering and precise tolerances are required.
In laid open Japanese Patent Application Ser. No. 56-185681 to K. Omori, published May 25, 1983, the rim of the end caps of an electroformed drum are raised to contact a driven rotating member which apparently maintains the spacing between the cylinder and some type of device. In order to reduce excessive wear, the end caps need to be made of metal which will result in increased mass and higher inertia characteristics.
Thus, there is a continuing need for lightweight photoreceptors that exhibit minimum run-out and are resistant to distortion.